Idiopathic inflammatory myopathy (polymyositis, dermatomyositis, and related disorders) is a family of inflammatory diseases in which disease-specific autoantibodies occur and for which there is considerable indirect evidence pointing to a viral etiology. We have over the past several years, seen and studied and collected serum, blood, and muscle specimens from well over 300 patients suspected of having myositis. We have collected epidemiologic information on many patients. We have completed an extremely sensitive search for candidate viruses by PCR in a subset of the specimens. We have extended studies of the disease-specific autoantibodies to show that antibodies to tRNA often are present early in the course of disease. We have cloned, sequenced, and expressed histidyl-tRNA synthetase and are analyzing its structure and promoter, and are in the process of trying to clone other targeted synthetases. We have extended the analysis of HLA antigens in the sets of myositis patients defined by autoantibodies using the sequence specific oligonucleotide hybridization/PCR method.